Daniel Lightfoot, Ph.D., Director of the Autism Tissue Program
Ricardo Dolmetsch, Ph.D. has a vision for autism research. Using pluripotent stem cell (iPSC) technology to create rare stem cells from other “common” cells of the human body cells, Dolmetsch and his lab at Stanford study neurodevelopmental disorders such as autism.
Unlike embryonic stem cells or adult stem cells which are isolated from existing and often difficult to obtain tissues, iPSC’s are “created” from easy to obtain and plentiful sources, such as skin or hair samples. This is accomplished through a unique process where cells are developmentally regressed to an earlier state.
To appreciate the concept of a stem cell, consider a seed. As a single cell it holds the potential to grow into an adult plant. It is a “stem cell” – one that can change or develop into any cell of the plant, from a leaf cell, to a flower cell or into a root cell. Through iPSC technology, this process is reversed. Scientists can developmentally regress an adult cell into an earlier cell like a seed. In short, scientists can turn a piece of a leaf into a seed, which could then grow into any cell of the plant. Though this does not at all imply that science can create a whole person from a skin sample, it does, however, allow researchers to easily create a variety of cells that can then be used for scientific study.
Once stem cells are created, they can be induced to develop into brain cells. For the first time, scientists are directly studying living brain cells in the lab. How these cells grow, interact, communicate, organize into groups and what helps or impairs these cells’ growth is now being more effectively studied. Additionally, stem cells have the unique ability to replicate without changing, meaning that from a single skin or hair sample many cells can be created. This allows a near limitless source of resources for scientific inquiry.
Dolmetsch shared this vision at a keynote presentation at IMFAR. He and his colleagues have now created an entire repository of stem cells from individuals with neurodevelopmental disorders. By comparing autism brain cells, with Timothy Syndrome and other disorders, the research team is not only learning about the differences among these conditions, but also the commonalities. Once the brain cell is created, it is possible to experiment with different compounds to determine whether they can restore neuronal function. Thus, stem cells provide a platform for drug screening. A deeper understanding of these disorders will also contribute more generally to a fundamental appreciation of how the human brain works.
A recent paper published in Cell Stem Cell reminds us that things are not always as they seem in biology. Autism Speaks’ funded projects led by co-authors Dr. Harley Kornblum and Dr. Janel Le Belle revealed that reactive oxygen species (ROS)—the cellular culprits creating oxidative stress—are actually necessary and present at higher levels early in the lives of brain cells.
Reactive oxygen species are a byproduct of normal cell metabolism. They can be damaging due to their chemically unstable nature. Peroxides are examples of ROS that result from the normal energy-production processes that take place inside the mitochondria in each cell. Typically, cells have a host of enzymes and cellular antioxidants to defend against an accumulation of ROS. However, environmental stressors such as ultraviolet radiation or overexposure to toxins can create more ROS than can be managed by an adult brain cell.
The research team was able to observe how young neurons not only used ROS to signal changes in cell processes, but needed more as they grew from neural stem cells into new neurons in the developing animal or human. Previously, it was believed that stem cells maintained low levels of ROS to protect the cells from damage, but neural stem cells seem to actually need higher levels of ROS to go on and make new neurons.
Certainly this is not the first time ROS has been shown to create positive effects. Previous research has shown that ROS can trigger the release of defense mechanisms against pathogens and initiate wound repair. However, more often, the build-up of ROS in cells is linked with cognitive decline in aging animals, when cellular mechanisms are less effective at removing ROS.
Other recent research has shown that by deleting genes that protect against a substantial increase in ROS, the young cells grow too much or “hyperproliferate”. The result is early brain overgrowth, much like has been reported for young children with autism. We don’t yet know at what stage in human fetal development higher levels of ROS would lead to larger brains, but this is one of many next stages of study in this line of questioning. From the studies in this report, it seems that the conversion of neural stem cells to differentiated neurons requires increased ROS, and suppressing it by various means also suppresses the creation of the new neurons from their stem cell predecessors.
Although the details of the “when” are as yet unknown with respect to early brain overgrowth due to increased ROS, the “how” is better understood. The pathway that leads to overgrowth is part of the well-studied PTEN pathway. We know a good bit about the molecular cascades in this pathway because the single gene mutations responsible for Tuberous Sclerosis complex (TSC)—one of the single gene disorders with a high proportion of individuals presenting with autism. PTEN acts as a suppressor of a pathway that encourages growth and the proliferation of new cells. Interestingly, Dr. Kornblum and his team showed that when ROS levels are reduced in developing brains, this pathway is less active and fewer new neurons are produced. Too much ROS leads to hyperproliferation and too little reduces the number of new cells produced.
This new research underscores the important role of ROS in the developing brain; however it is not yet clear whether antioxidant therapy would be beneficial or harmful during normal development or even in the fetuses at higher risk for autism. However, this is something that Dr. Kornblum and his team hope to explore, saying “The key here is that we cannot think of antioxidants as either universally good or universally bad.”
Janel E. Le Belle, Nicolas M. Orozco, Andres A. Paucar, Jonathan P. Saxe, Jack Mottahedeh, April D. Pyle, Hong Wu, and Harley I. Kornblum. (2011) Cell Stem Cell. Proliferative Neural Stem Cells Have High Endogenous ROS Levels that Regulate Self-Renewal and Neurogenesis in a PI3K/Akt-Dependant Manner. 8: 59–71. DOI 10.1016/j.stem.2010.11.028
Science advances in fits and starts. Part of Autism Speaks’ role as an advocacy and science funding organization is to find ways to identify and advance the science that could lead to improvements in the lives of those struggling with Autism Spectrum Disorders. New ideas bubble up frequently, however few mechanisms exist to support the exploration of unique and novel ideas. The burden of evidence required to secure funding for a great idea is very high and often dissuades researchers from pushing for greater innovation and out-of-the-box thinking, resulting in research that is “safe” and moving at a pace that is slower than any of us would like.
To address this need, Autism Speaks has launched the Suzanne and Bob Wright Trailblazer Awards. The Trailblazer Awards commemorate Autism Speaks’ fifth anniversary and honors our organization’s pioneering founders, Suzanne and Bob Wright. We are grateful to the generous donors who have made contributions to support this special research innovation fund.
Trailblazer Awards provide seed funding to test out a novel idea or approach that has the potential to transform some aspect of autism research. Importantly, applications for these awards are accepted and reviewed on a rolling basis so new ideas are evaluated quickly and those ripe for this mechanism meet with funding quickly. The three funded projects summarized below will receive up to $100,000 for one year and each addresses a point of need as outlined in Autism Speaks’ Strategic Plan.
Mitochondria have been the focus of considerable buzz in autism research recently. However, the reports on mitochondria’s control of cellular energy processes only scratch the surface of the complex web of cellular activities that these organelles orchestrate [see also mitochondrial and fever story]. Robert Naviaux, MD., Ph.D., (UCSD) and his colleagues are grateful for the opportunity to pursue research on how mitochondrial metabolites may play a role in brain inflammation. “The Trailblazer award gives our lab the support to bring together 3 world-class groups to study the role of mitochondria in autism. If successful, our results will provide the foundation for both fresh new therapies, but also for additional studies that clarify the role of mitochondria and the environment in the cause of autism,” said Naviaux.
The idea Dr. Naviaux brought to Autism Speaks focuses on a product of the mitochondria, called ATP, that is required for the development of brain cells and their communication with each other. For cells to function properly, very specific quantities of ATP are required around the brain cells. Naviaux will explore whether mitochondrial dysfunction, which can result in high concentrations of ATP in the space between cells, stimulates inflammation in the brain, and also alters connectivity between neurons. Importantly, Dr. Naviaux and his colleagues will also test a compound that works against the effects of high concentrations of ATP as a potential therapy. The effects of manipulating ATP and the pathways it tickles will be tested in a well-established mouse model for autism so the effects at both the cellular as well as behavior level can be compared before and after treatment. Read the grant abstract.
Phil Schwartz, Ph.D. (Children’s Hospital of Orange County) is building a unique resource that aims to bring personalized medical solutions to individuals living with autism. The technology now exists to take a small sample of skin tissue and from that create stem cells that can be used to make personalized copies of any type of cell in the body. Of interest to autism, of course, are brain cells. Schwartz and his colleagues have not only created neurons from skin cells, but they are also pioneering a method to incorporate them into living mouse brains so they can evaluate how these human-derived cells function as part of a circuit. Dr. Schwartz is extremely enthusiastic about this research, saying “If this research is successful, we will be able to test, in animal model of autism based on human cells, novel therapeutic approaches and examine those putative therapies on bona fide human cells in an in vivo setting. This is about as close as we can get to clinical trials without actually using humans!”
Dr. Schwartz and his colleague, Dr. Diane O’Dowd, are aiming to build the largest bank of stem cells made from skin (called induced pluripotent stem cells) for autism research. If these new techniques prove successful, there will be a unique new tool for individualizing autism research unlike any currently available today. Read the grant abstract.
Earlier this year, Antonio Persico, M.D. (Università Campus Bio-Medico di Roma) published results demonstrating that a class of viruses, called polyomaviruses, were found significantly more often in postmortem brain tissue of persons with ASD than in individuals with typical development. The presence of these viruses presents a possible mechanism for the persistent immune activation seen in brain tissue of individuals with autism, originally reported by Vargas and colleagues in 2005. How did the viruses get into the brains of these people and what does this mean? Dr. Persico thinks that at least some forms of autism can be explained by the passing of a virus “vertically”, that is from parent to child, by incorporating itself into the genetic material in the sperm or egg. The presence of this virus is unknown to the carrier without explicit testing (ie. these individuals do not appear to be acutely ill) and can remain quietly.
Polyomaviruses have been shown to cause autoimmune disorders, which have been correlated with the first degree relatives of individuals with autism. If an early and unresolved polyomavirus infection was present in children with autism, the researchers would expect to see evidence of persistent immune activation for these viruses outside the central nervous system. Indeed, children with autism had lower levels of certain types of polyomavirus in urine than did typically-developing children. These polyomaviruses result in common childhood infections and low levels of virus in children with autism is indirect evidence for immune activation against these specific viruses. This clue led Dr. Persico and his colleagues to hypothesize that polyomavirus was likely passed from a parent and not acquired later in life. “What is transmitted from parent to offspring may not be human DNA but rather a virus. This idea could explain high heritability as well as systemic signs and symptoms of ASD, such as overgrowth of the entire body, immune and biochemical abnormalities. The translational potential of this project in terms of diagnostics, prevention and therapeutics is self-evident,” says Persico. Read the grant abstract.
Taken together, these new grants and the Trailblazer funding mechanism represent a bold new effort to attract and support the most innovative ideas that have the potential to transform our understanding of autism research. We anxious await to hear from each of these researchers to learn what they discover.
Read a press release about all of the science grants announced by Autism Speaks in December 2010.
Reference: Vargas DL, Nascimbene C, Krishnan C, Zimmerman AW, Pardo CA. Neuroglial activation and neuroinflammation in the brain of patients with autism. Ann Neurol. 2005 Jan;57(1):67-81. Erratum in: Ann Neurol. 2005 Feb;57(2):304.